1. Field of the Invention
The present invention relates to a gas cluster ion beam emitting apparatus emitting a gas cluster ion to a processing object to subject the processing object to desired processing and a method for ionization of a gas cluster.
2. Related Background Art
For the purpose of the surface rinsing of an electric device, surface modification by ion injection, formation of a thin film or the like, various kinds of vapor phase reaction methods have been developed, and for example, processes such as sputtering, vacuum deposition, CVD and ion beam vapor deposition have been brought into practical use. However, in these methods, the degree to which the surface of a processing object is damaged or degraded may be relatively high. For alleviating this problem, the gas cluster ion beam (GCIB) technique for emitting a gas cluster to a processing object as an ion beam is under development. Here, “gas cluster” is a plurality of gas atoms or molecules clustering in a massive form, and “gas cluster ion” is a gas cluster ionized. Further, “gas cluster ion beam” is a plurality gas cluster ions in a beam form.
Japanese Patent Application Laid-Open No. H08-120470 discloses an apparatus emitting such a gas cluster ion beam to a target. The configuration of this apparatus will be described below with reference to FIG. 6.
The apparatus shown in FIG. 6 is an apparatus subjecting the processing object to fine polishing processing, and has two vacuum chambers 501 and 502 to which vacuum pumps 511 and 512 are connected, respectively. A source gas supplied from a gas bomb 503 is jetted from a nozzle 504 at a supersonic speed and generates a gas cluster through adiabatic expansion. The generated gas cluster is shaped into a beam form when passing though a skimmer 505, and supplied to an ionization portion 507. In this ionization portion 507, thermal electrons generated when a filament 506 is heated are collided with a gas cluster to perform ionization, whereby the gas cluster becomes a gas cluster ion. The gas cluster ion is then accelerated by an electric field in an acceleration portion 508, and further, clusters are screened according to size by a deceleration field in a deceleration electric field 509. The screened gas cluster ion is accelerated again in the acceleration portion 513, and emitted to a processing object 510 to which a high voltage has been applied.
In a fine polishing processing apparatus having such a configuration, when a gas cluster ion emitted to the processing object 510 is collided and thereby collapses, clustering constituent atoms (or molecules) are scattered to spread over the surface of the processing object 510. Thus, lateral polishing (also called “lateral sputtering”) to the surface of the processing object 510 can be performed well.
In addition to the above-mentioned document, Japanese Patent Application Laid-Open No. H08-127867 and Patent Application Laid-Open No. H09-41122 (U.S. Publication No. US2002015803) disclose a thin film formation method using a gas cluster ion beam. Further, National Publication of International Patent Application No. 2003-520393 (U.S. Publication No. US2002162508) discloses a configuration in which a filament is placed near a path of gas cluster emitted so that thermal electrons are vigorously collided with a gas cluster.
However, if for example, a reaction gas (e.g. SF6, O2) is used for a gas for a gas cluster in the case of the configuration in which the gas cluster is ionized using a filament, a problem such that the filament is worn at an early stage due to the influence of such a gas arises. This problem is more significant when the filament is placed near the path of gas cluster emitted. The problem of the filament being worn means that a normal operation cannot be performed over a long time period in the emitting apparatus. From another point of view, time being spent for replacement of the filament causes a reduction in productivity.
Further, in the configuration in which a gas cluster is ionized by thermal electrons from the filament, its efficiency is relatively low, and a more or less improvement is achieved by, for example, making some contrivance on the shape of the filament, but it is not adequate.
Thus, it is an object of the present invention to provide a gas cluster ion beam emitting apparatus capable of normally operating over a long time period. It is another object of the present invention to provide a gas cluster ion beam emitting apparatus and a method for ionization of a gas cluster, which can efficiently ionize a gas cluster.